User station for a serial bus system, and method for communicating in a serial bus system

ABSTRACT

A user station for a serial bus system. The user station includes a communication control device for controlling a communication of the user station with at least one other user station, and a transceiver device for transmitting a transmission signal, generated by the communication control device, onto a bus, so that for a message that is exchanged between user stations of the bus system, the bit time of a signal transmitted onto the bus in the first communication phase is different from a bit time of a signal transmitted in the second communication phase. The communication control device generates the transmission signal according to a frame in which a field for a header check sum and a field for a frame check sum are provided, and computers the header check sum from all bits in the header of a frame that is formed for the message, except fixed stuff bits.

FIELD

The present invention relates to a user station for a serial bus system,and a method for communicating in a serial bus system that operates witha high data rate and a high level of error robustness.

BACKGROUND INFORMATION

For the communication between sensors and control units, for example invehicles, a bus system is frequently preferred instead of apoint-to-point connection. With the increasing number of functions of atechnical facility or of a vehicle, the data traffic in the bus systemalso increases. Moreover, there is a continual requirement for the datato be transmitted from the transmitter to the receiver more quickly thanpreviously.

At the present time, in vehicles a bus system is used in theintroduction phase, in which data are transmitted as messages under theISO 11898-1:2015 standard, as a CAN protocol specification with CAN FD.The messages are transmitted between the bus users of the bus system,such as the sensor, control unit, transducer, etc.

In CAN FD, one of the advantages is that the length of a frame that istransmitted via the bus is dynamically changeable. Among other things,this is due to the fact that the length of the data field fortransmitting the useful data does not always have to be equal to themaximum possible length of 64 bytes, but instead may be appropriatelyshortened when there are fewer useful data to be transmitted. As aresult, the bus is blocked for no longer than necessary by one of themessages to be transmitted.

Therefore, in CAN FD the variable data field length is indicated in aDLC field. If a bit error occurs here, the receiver may decode anincorrect frame length, and therefore checks the check sum (cyclicredundancy check (CRC)) at the wrong location. It is then a matter ofluck as to whether an error is detected based on the check sum (CRCerror).

Another reason for the dynamically changing length of a CAN FD frameinvolves a bit stuffing rule. According to this rule, after fiveidentical bits a bit inverse thereto is to be inserted into a CAN FDmessage. Therefore, in the field for the check sum (CRC field) a stuffbit counter is necessary in which the number of dynamically insertedstuff bits is entered. However, this stuff bit counter results incomplexity and data overhead. As a result, the transmittable net datarate drops, which slows down the communication in the bus system.

SUMMARY

An object of the present invention is to provide a user station for aserial bus system, and a method for transmitting a message in a serialbus system, which solve the above-mentioned problems. In particular,example embodiments of the present invention provide a user station fora serial bus system, and a method for communicating in a serial bussystem in which the disadvantages of the check sum safeguarding do notoccur, so that a high data rate and an increase in the quantity of theuseful data per frame may be achieved with great flexibility and with ahigh level of error robustness of the communication.

The object may be achieved by a user station for a serial bus systemhaving the features of an example embodiment of the present invention.In accordance with an example embodiment of the present invention, theuser station includes a communication control device for controlling acommunication of the user station with at least one other user stationof the bus system, and a transceiver device for transmitting atransmission signal, generated by the communication control device, ontoa bus of the bus system, so that for a message that is exchanged betweenuser stations of the bus system, the bit time of a signal transmittedonto the bus in the first communication phase is different from a bittime of a signal transmitted in the second communication phase, thecommunication control device being designed to generate the transmissionsignal according to a frame in which a field for a header check sum anda field for a frame check sum are provided, and the communicationcontrol device being designed to compute the header check sum from allbits in the header of a frame that is formed for the message, with theexception of fixed stuff bits that have been inserted into the header ofthe frame according to a fixed bit stuffing rule, according to which afixed stuff bit is to be inserted after a fixed number of bits.

Due to the example embodiment of the user station, in a frame that istransmitted on the bus in order to exchange messages between the userstations of the bus system, a field containing the length of the frameis safeguarded. The correct length of the frame is thus always ensured.As a result, a receiver of the frame may always decode the correct framelength, and therefore may check the check sum (cyclic redundancy check(CRC)) at the end of the frame at the correct location. Errors in thecommunication in the bus system may thus be quickly and reliablydetected. This means that the residual error probability issignificantly decreased. The residual error probability indicates theprobability of a frame being accepted as correct despite an error.

In addition, no stuff bit counter is necessary for safeguarding thelength of the frame, carried out with the user station. This reduces thecomplexity of creating a frame in the transmitting user station, andreduces the complexity of evaluating a frame in a receiving userstation, as well as the overhead of data to be transmitted. As a result,the transmittable net data rate increases, which speeds up thecommunication in the bus system.

As a result, by use of the user station, transmission and reception ofthe frames may be ensured with great flexibility with regard toinstantaneous results during operation of the bus system and with a lowerror rate, even with an increased volume of useful data per frame.

By use of the user station in the bus system, it is thus possible inparticular to maintain an arbitration known from CAN in a firstcommunication phase and still increase the transmission rateconsiderably compared to CAN or CAN FD.

The method carried out by the user station may also be used when atleast one CAN user station and/or at least one CAN FD user station thattransmit(s) messages according to the CAN protocol and/or CAN FDprotocol are/is present in the bus system.

Advantageous further embodiments of the user station are disclosedherein.

According to one particular embodiment variant of the present invention,the communication control device is designed to provide the header checksum in the transmission signal prior to a data field.

The communication control device is optionally designed to include thefixed stuff bits in the frame when computing the header check sum.

According to one exemplary embodiment, the communication control deviceis designed to compute the frame check sum from all bits that aresituated in a frame, formed for the message, prior to the frame checksum, all fixed stuff bits that have been inserted into the frameaccording to a fixed bit stuffing rule, according to which a fixed stuffbit is to be inserted after a fixed number of bits, either beingincluded or not included.

According to one variant, the communication control device is designedto compute the frame check sum from all bits that are situated in thefield for the header check sum and in the data field of the frame thatis formed for the message.

Alternatively, the communication control device may be designed tocompute the frame check sum from all bits that are situated in the datafield of the frame that is formed for the message.

According to one exemplary embodiment of the present invention, theframe that is formed for the message includes an additional field thatis situated prior to the field for the header check sum, and thecommunication control device being designed to insert informationconcerning the number of dynamic stuff bits in the frame into theadditional field.

The communication control device is possibly designed to configure theadditional field as a field having a fixed length, in which the numberof stuff bits, as information concerning the number of dynamic stuffbits, is inserted into the frame. Alternatively, the communicationcontrol device is possibly designed to select the length of theadditional field as a function of how many dynamic stuff bits areinserted into the frame, so that the field for the header check sum isalways expected after the same number of bits after the start of theframe on the bus.

The user station may also include a check sum unit for determining astarting value for computing the header check sum, in such a way thatthe temporary value of the header check sum up to the FDF bit cannotassume the value zero.

It is possible for the frame that is formed for the message to have adesign that is compatible with CAN FD.

It is possible for the communication control device to be designed togenerate the transmission signal according to a frame in which the fieldfor a frame check sum is provided, but the field for the header checksum is not provided, and for the communication control device to bedesigned to apply a fixed bit stuffing rule in the entire frame,according to which a fixed stuff bit is to be inserted after a fixednumber of bits.

Alternatively or additionally, the communication control device isoptionally designed to provide an identifier in the frame whichindicates the priority for transmitting the associated message onto thebus, the number of bits for the identifier being freely selectable.

Alternatively or additionally, the communication control device may bedesigned to provide an interval of 0 bit or 1 bit between successiveframes in the transmission signal.

It is possible that in the first communication phase, it is negotiatedwhich of the user stations of the bus system in the subsequent secondcommunication phase obtains, at least temporarily, exclusive,collision-free access to the bus.

The user station described above may be part of a bus system which alsoincludes a bus and at least two user stations that are connected to oneanother via the bus in such a way that they may communicate seriallywith one another. At least one of the at least two user stations is auser station described above.

Moreover, the object stated above may be achieved by a method forcommunicating in a serial bus system according to example embodiments ofthe present invention. The method is carried out with a user station ofthe bus system that includes a communication control device and atransceiver device. In accordance with an example embodiment of thepresent invention, the method includes the steps: controlling, via thecommunication control device, a communication of the user station withat least one other user station of the bus system, and transmitting, viathe transceiver device, a transmission signal, generated by thecommunication control device, onto a bus of the bus system, so that fora message that is exchanged between user stations of the bus system, thebit time of a signal that is transmitted onto the bus in the firstcommunication phase is different from a bit time of a signal that istransmitted in the second communication phase, the communication controldevice generating the transmission signal according to a frame in whicha field for a header check sum and a field for a frame check sum areprovided, and the communication control device computing the headercheck sum from all bits in the header of a frame that is formed for themessage, with the exception of fixed stuff bits that have been insertedinto the header of the frame according to a fixed bit stuffing rule,according to which a fixed stuff bit is to be inserted after a fixednumber of bits.

The method yields the same advantages as stated above with regard to theuser station.

Further possible implementations of the present invention also includecombinations, even if not explicitly stated, of features or specificembodiments described above or discussed below with regard to theexemplary embodiments. Those skilled in the art will also add individualaspects as enhancements or supplements to the particular basic form ofthe present invention, in view of the disclosure herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail below withreference to the figures, and based on exemplary embodiments.

FIG. 1 shows a simplified block diagram of a bus system according to afirst exemplary embodiment.

FIG. 2 shows a diagram for illustrating the design of a message that maybe transmitted from a user station of the bus system according to thefirst exemplary embodiment.

FIG. 3 shows a simplified schematic block diagram of a user station ofthe bus system according to the first exemplary embodiment.

FIG. 4 shows a temporal profile of bus signals CAN FX_H and CAN FX_L forthe user station according to the first exemplary embodiment.

FIG. 5 shows a temporal profile of a differential voltage VDIFF of bussignals CAN FX_H and CAN FX_L for the user station according to thefirst exemplary embodiment.

FIG. 6 shows a diagram for illustrating the design of a message that maybe transmitted from a user station of the bus system according to asecond exemplary embodiment.

FIG. 7 shows a diagram for illustrating the design of a message that maybe transmitted from a user station of the bus system according to athird exemplary embodiment.

FIG. 8 shows a diagram for illustrating a further aspect of the presentinvention, namely, the introduction of multiple identifiers into the CANFX frame. In FIG. 8 this aspect is illustrated based on theabove-described first exemplary embodiment from FIG. 2. This aspect ofthe present invention may also be correspondingly applied to the secondexemplary embodiment illustrated in FIG. 6, and the third exemplaryembodiment illustrated in FIG. 7.

Unless stated otherwise, identical or functionally equivalent elementsare provided with the same reference numerals in the figures.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows as an example a bus system 1 that is in particular thebasis for the design of a CAN bus system, a CAN FD bus system, a CAN FXbus system, and/or modifications thereof, as described below. Bus system1 may be used in a vehicle, in particular a motor vehicle, an aircraft,etc., or in a hospital, and so forth.

In FIG. 1, bus system 1 includes a plurality of user stations 10, 20,30, each of which is connected to a first bus wire 41 and a second buswire 42 at a bus 40. Bus wires 41, 42 may also be referred to as CAN_Hand CAN_L or CAN FX_H and CAN FX_L, and are used for electrical signaltransmission after coupling in the dominant levels or generatingrecessive levels for a signal in the transmission state. Messages 45, 46in the form of signals are serially transmittable between individualuser stations 10, 20, 30 via bus 40. If an error occurs during thecommunication on bus 40, as illustrated by the serrated dark block arrowin FIG. 1, an error frame 47 (error flag) may optionally be transmitted.User stations 10, 20, 30 are, for example, control units, sensors,display devices, etc., of a motor vehicle.

As shown in FIG. 1, user station 10 includes a communication controldevice 11, a transceiver device 12, and a check sum unit 15. Userstation 20 includes a communication control device 21, a transceiverdevice 22, and a check sum unit 25. User station 30 includes acommunication control device 31, a transceiver device 32, and a checksum unit 35. Transceiver devices 12, 22, 32 of user stations 10, 20, 30are each directly connected to bus 40, although this is not illustratedin FIG. 1.

Communication control devices 11, 21, 31 are each used for controlling acommunication of particular user station 10, 20, 30 via bus 40 with atleast one other user station of user stations 10, 20, 30 connected tobus 40.

Communication control devices 11, 31 create and read first messages 45,which are modified CAN messages 45, for example. Modified CAN messages45 are built up based on a CAN FX format, described in greater detailwith reference to FIG. 2, and in which particular check sum unit 15, 35is used. Communication control devices 11, 31 may also be designed toprovide a CAN FX message 45 or a CAN FD message 46 for transceiverdevice 32 or receive it from same, as needed. Particular check sum units15, 35 may also be used. Communication control devices 11, 31 thuscreate and read a first message 45 or second message 46, first andsecond messages 45, 46 differing by their data transmission standard,namely, CAN FX or CAN FD in this case.

Communication control device 21 may be designed as a conventional CANcontroller according to ISO 11898-1:2015, i.e., as a CAN FD-tolerantconventional CAN controller or a CAN FD controller. Communicationcontrol device 21 creates and reads second messages 46, for example CANFD messages 46. CAN FD messages 46 may include 0 to 64 data bytes, whichare also transmitted at a much faster data rate than with a conventionalCAN message. In particular, communication control device 21 is designedas a conventional CAN FD controller.

Transceiver device 22 may be designed as a conventional CAN transceiveraccording to ISO 11898-1:2015 or as a CAN FD transceiver. Transceiverdevices 12, 32 may be designed to provide messages 45 according to theCAN FX format or messages 46 according to the present CAN FD format forassociated communication control device 11, 31 or receive the messagesfrom same, as needed.

A formation and then transmission of messages 45 having the CAN FXformat, in addition to the reception of such messages 45, is achievableby use of the two user stations 10, 30.

FIG. 2 shows for message 45 a CAN FX frame 450, which is provided bycommunication control device 11 for transceiver device 12 fortransmitting onto bus 40. In the present exemplary embodiment,communication control device 11 creates frame 450 so as to be compatiblewith CAN FD, as also illustrated in FIG. 2. The same analogously appliesfor communication control device 31 and transceiver device 32 of userstation 30.

According to FIG. 2, for the CAN communication on bus 40, CAN FX frame450 is divided into different communication phases 451, 452, namely, anarbitration phase 451 and a data phase 452. Frame 450 includes anarbitration field 453, a control field 454, a data field 455, a checksum field 456 for a check sum F_CRC, a synchronization field 457, and anacknowledgment field 458.

In arbitration phase 451, with the aid of an identifier ID inarbitration field 453, bitwise negotiation is carried out between userstations 10, 20, 30 concerning which user station 10, 20, 30 would liketo transmit message 45, 46 having the highest priority, and thereforefor the next time period for transmitting in subsequent data phase 452obtains exclusive access to bus 40 of bus system 1. A physical layer,similarly as with CAN and CAN FD, is used at least in arbitration phase451. The physical layer corresponds to the bit transmission layer orlayer 1 of the conventional Open Systems Interconnection (OSI) model.

An important point during phase 451 is that the conventional CSMA/CRmethod is used, which allows simultaneous access of user stations 10,20, 30 to bus 40 without destroying higher-priority message 45, 46. Itis thus possible to add further bus user stations 10, 20, 30 to bussystem 1 in a relatively simple manner, which is very advantageous.

Consequently, the CSMA/CR method must provide so-called recessive stateson bus 40, which may be overwritten by other user stations 10, 20, 30with dominant states on bus 40. In the recessive state, high-impedanceconditions prevail at individual user station 10, 20, 30, which incombination with the parasites of the bus wiring result in longer timeconstants. This results in a limitation of the maximum bit rate of thepresent-day CAN FD physical layer to approximately 2 megabits per secondat the present time during actual vehicle use.

In data phase 452, in addition to a portion of control field 454, theuseful data of the CAN FX frame or of message 45 from data field 455,and check sum field 456 for check sum F_CRC, are transmitted.

A sender of message 45 starts a transmission of bits of data phase 452onto bus 40 only after user station 10, as the sender, has won thearbitration, and user station 10, as the sender, thus has exclusiveaccess to bus 40 of bus system 1 for the transmission.

In general, in the bus system with CAN FX, in comparison to CAN or CANFD in particular the following differing properties may be achieved:

-   a) taking over and optionally adapting proven properties that are    responsible for the robustness and user-friendliness of CAN and CAN    FD, in particular a frame structure including identifiers and    arbitration according to the CSMA/CR method,-   b) increasing the net data transmission rate to approximately 10    megabits per second,-   c) increasing the quantity of the useful data per frame to    approximately 4 kbytes.

As illustrated in FIG. 2, in arbitration phase 451 user station 10partially uses as the first communication phase, in particular up to andincluding the FDF bit, a format known from CAN/CAN FD according to ISO11898-1:2015. In contrast, beginning with the FDF bit in the firstcommunication phase and in the second communication phase (data phase452), user station 10 uses a CAN FX format, as described below.

In the present exemplary embodiment, CAN FX and CAN FD are compatible.The res bit known from CAN FD, referred to below as the FXF bit, isutilized for switching from the CAN FD format over to the CAN FX format.Therefore, the frame formats of CAN FD and CAN FX are identical up tothe res bit. A CAN FX user station, i.e., user stations 10, 30 here,also support(s) CAN FD.

As an alternative to frame 450 shown in FIG. 2, in which an identifierincluding 11 bits is used, a CAN FX expanded frame format is optionallypossible in which an identifier including 29 bits is used. Except forthe FDF bit, this is identical to the known CAN FD expanded frame formatfrom ISO 11898-1:2015.

According to FIG. 2, frame 450 from the SOF bit up to and including theFDF bit is identical to the CAN FD base frame format according to ISO11898-1:2015. Therefore, the structure is not further explained here.Bits illustrated with a thick bar at their lower line in FIG. 2 aretransmitted in frame 450 as dominant. Bits illustrated with a thick barat their upper line in FIG. 2 are transmitted in frame 450 as recessive.

In general, two different stuffing rules are applied in the generationof frame 450. Except for the FXF bit in control field 454, the dynamicbit stuffing rule from CAN FD applies, so that an inverse stuff bit isto be inserted after 5 identical bits in succession. A fixed stuffingrule applies after an FX bit in control field 454, so that a fixed stuffbit is to be inserted after a fixed number of bits. Alternatively,instead of only one stuff bit, 2 or more bits may be inserted as fixedstuff bits.

In frame 450, the FDF bit is directly followed by the FXF bit, whichfrom the position corresponds to the “res bit” in the CAN FD base frameformat, as mentioned above. If the FXF bit is transmitted as 1, i.e.,recessive, it thus identifies frame 450 as a CAN FX frame. For a CAN FDframe, communication control device 11 sets the FXF bit as 0, i.e.,dominant.

In frame 450, the FXF bit is followed by a resFX bit, which is adominant bit for future use. For frame 450, the resFX bit must betransmitted as 0, i.e., dominant. However, if user station 10 receives aresFX bit as 1, i.e., recessive, receiving user station 10 goes into aprotocol exception state, for example, as carried out with a CAN FDmessage 46 for res=1. The resFX bit could also be defined the oppositeway, i.e., that it must be transmitted as 1, i.e., recessive, so thatfor a dominant resFX bit the receiving user station goes into theprotocol exception state.

In frame 450, the FXF bit is followed by a sequence BRS AD, in which apredetermined bit sequence is encoded. This bit sequence allows a simpleand reliable switch from the arbitration bit rate of arbitration phase451 over to the data bit rate of data phase 452. For example, the bitsequence of BRS AD is made up of a recessive arbitration bit followed bya dominant data bit. In this example, the bit rate may be switched overat the edge between the two stated bits.

In frame 450, sequence BRS AD is followed by a DLC field into which datalength code DLC, which indicates the number of bytes in data field 455of frame 450, is inserted. Data length code DLC may assume any valuefrom 1 up to the maximum length of data field 455 or the data fieldlength. If the maximum data field length is in particular 2048 bits,data length code DLC requires 11 bits, under the assumptions that DLC=0means a data field length that includes 1 byte, and DLC=2047 means adata field length that includes 2048 bytes. Alternatively, data field455 having the length 0 could be allowed, as with CAN, for example.DLC=0 would encode, for example, the data field length with 0 byte. With11 bits, for example, the maximum encodable data field length is then(2{circumflex over ( )}11)−1=2047.

In frame 450, the DLC field is followed by a header check sum H_CRC. Theheader check sum is a check sum for safeguarding the header of frame450, i.e., all bits from the start of frame 450 including the SOF bit tothe start of header check sum H_CRC, including all dynamic, andoptionally, fixed, stuff bits up to the start of header check sum H_CRC.The length of header check sum H_CRC, and thus of the check sumpolynomial according to cyclic redundancy check CRC, is to be selectedcorresponding to the desired Hamming distance. For a data length codeDLC of 11 bits, the data word to be safeguarded by header check sumH_CRC is longer than 27 bits. Therefore, in order to achieve a Hammingdistance of 6, the polynomial of header check sum H_CRC must be at least13 bits long. The computation of header check sum H_CRC is described ingreater detail below.

In frame 450, header check sum H_CRC is followed by data field 455. Datafield 455 is made up of 1 to n data bytes, where n is, for example, 2048bytes or 4096 bytes or some other arbitrary value. Alternatively, a datafield length of 0 is possible. The length of data field 455 is encodedin the DLC field, as described above.

In frame 450, data field 455 is followed by a frame check sum F_CRC.Frame check sum F_CRC is made up of the bits of frame check sum F_CRC.The length of frame check sum F_CRC, and thus of the CRC polynomial, isto be selected corresponding to the desired Hamming distance. Framecheck sum F_CRC safeguards entire frame 450. Alternatively, only datafield 455 is optionally safeguarded with frame check sum F_CRC. Thecomputation of frame check sum F_CRC is described in greater detailbelow.

In frame 450, frame check sum F_CRC is followed by a sequence BRS DA inwhich a predetermined bit sequence is encoded. This bit sequence allowsa simple and reliable switch from the data bit rate of data phase 452over to the arbitration bit rate of arbitration phase 451. For example,the bit sequence of BRS DA is made up of a recessive arbitration bitfollowed by a dominant data bit. In this example, the bit rate may beswitched over at the edge between the two stated bits.

In frame 450, sequence BRS DA is followed by a sync field in which asynchronization pattern (sync pattern) is kept. The synchronizationpattern is a bit pattern that allows a receiving user station 10, 30 todetect the start of arbitration phase 451 after data phase 452. Thesynchronization pattern allows receiving user station 10, 30, whichcannot detect the correct length of data field 455, for example due toan erroneous header check sum H_CRC, to synchronize. These user stationsmay subsequently transmit a “negative acknowledge” in order tocommunicate the incorrect reception. This is very important inparticular when CAN FX no longer allows error frames 47 (error flags) indata field 455.

In frame 450, the sync field is followed by an acknowledgment (ACK)field made up of multiple bits, namely, in the example of FIG. 2, an ACKbit, an ACK dlm bit, a NACK bit, and a NACK dlm bit. The NACK bit andthe NACK dlm bit are optional bits. Receiving user stations 10, 30transmit the ACK bit as dominant when they have correctly received frame450. The transmitting user station transmits the ACK bit as recessive.Therefore, the bit in frame 450 originally transmitted onto bus 40 maybe overwritten by receiving user stations 10, 30. The ACK dlm bit istransmitted as a recessive bit, which is used for separation from otherfields. The NACK bit and the NACK dlm bit are used so that a receivinguser station may signal an incorrect reception of frame 450 on bus 40.The function of the bits is the same as that of the ACK bit and the ACKdlm bit.

In frame 450, the acknowledgment (ACK) field is followed by an end field(end of frame (EOF)). The bit sequence of end field EOF is used todenote the end of frame 450. End field EOF ensures that 8 recessive bitsare transmitted at the end of frame 450. This is a bit sequence thatcannot occur within frame 450. As a result, the end of frame 450 may bereliably detected by user stations 10, 20, 30.

End field EOF has a length that is different, depending on whether adominant bit or a recessive bit has been observed in the NACK bit. Ifthe transmitting user station has received the NACK bit as dominant, endfield EOF includes 7 recessive bits. Otherwise, end field EOF is only 5recessive bits long.

In frame 450, end field EOF is followed by an interframe space IFS. Thisinterframe space IFS is designed according to ISO 11898-1:2015, as withCAN FD.

FIG. 3 shows the basic design of user station 10 together withcommunication control device 11, transceiver device 12, and check sumunit 15, which is part of communication control device 11. User station30 has a design similar to that shown in FIG. 3, except that check sumunit 35 according to FIG. 1 is situated separately from communicationcontrol device 31 and transceiver device 32. Therefore, user station 30is not separately described.

According to FIG. 3, in addition to communication control device 11 andtransceiver device 12, user station 10 includes a microcontroller 13with which control device 11 is associated, and a systemapplication-specific integrated circuit (ASIC) 16, which alternativelymay be a system base chip (SBC) on which multiple functions necessaryfor an electronics assembly of user station 10 are combined. In additionto transceiver device 12, an energy supply device 17 that suppliestransceiver device 12 with electrical energy is installed in system ASIC16. Energy supply device 17 generally supplies a voltage CAN_Supply of 5V, as needed. Additionally or alternatively, energy supply device 17 maybe designed as a power source.

Check sum unit 15 includes a header check sum block 151 and a framecheck sum block 152, described in greater detail below. A starting value1511 is at least temporarily stored in header check sum block 151.

Transceiver device 12 also includes a transmitter 121 and a receiver122. Even though transceiver device 12 is consistently referred tobelow, it is alternatively possible to provide receiver 122 in aseparate device externally from transmitter 121. Transmitter 121 andreceiver 122 may be designed as a conventional transceiver device 22.Transmitter 121 may in particular include at least one operationalamplifier and/or one transistor. Receiver 122 may in particular includeat least one operational amplifier and/or one transistor.

Transceiver device 12 is connected to bus 40, or more precisely, to itsfirst bus wire 41 for CAN_H or CAN FX_H and its second bus wire 42 forCAN_L or CAN FX_L. The supplying of voltage for energy supply device 17for supplying first and second bus wires 41, 42 with electrical energy,in particular with voltage CAN_Supply, takes place via at least oneterminal 43. The connection to ground or CAN_GND is achieved via aterminal 44. First and second bus wires 41, 42 are terminated via aterminating resistor 49.

In transceiver device 12, first and second bus wires 41, 42 are not justconnected to transmitter 121 and to receiver 122, even though theconnection in FIG. 3 is not shown for simplification.

During operation of bus system 1, transmitter 121 converts atransmission signal TXD or TxD of communication control device 11 intocorresponding signals CAN FX_H and CAN FX_L for bus wires 41, 42, andtransmits these signals CAN FX_H and CAN FX_L onto bus 40 at theterminals for CAN_H and CAN_L.

According to FIG. 4, receiver 122 forms a reception signal RXD or RxDfrom signals CAN FX_H and CAN FX_L that are received from bus 40, andpasses it on to communication control device 11, as shown in FIG. 3.With the exception of an idle or standby state, transceiver device 12with receiver 122 during normal operation always listens to atransmission of data or messages 45, 46 on bus 40, in particularregardless of whether or not transceiver device 12 is the sender ofmessage 45.

According to the example from FIG. 4, signals CAN FX_H and CAN FX_L, atleast in arbitration phase 451, include dominant and recessive buslevels 401, 402, as known from CAN. A difference signal VDIFF=CANFX_H−CAN FX_L, shown in FIG. 5, is formed on bus 40. The individual bitsof signal VDIFF with bit time t_bt may be recognized using a receptionthreshold of 0.7 V. In data phase 452 the bits of signals CAN FX_H andCAN FX_L are transmitted more quickly, i.e., with a shorter bit timet_bt, than in arbitration phase 451. Thus, signals CAN FX_H and CAN FX_Lin data phase 452 differ from conventional signals CAN_H and CAN_L, atleast in their faster bit rate.

The sequence of states 401, 402 for signals CAN FX_H, CAN FX_L in FIG. 4and the resulting pattern of voltage VDIFF from FIG. 5 are used only forillustrating the function of user station 10. The sequence of datastates for bus states 401, 402 is selectable as needed.

In other words, transmitter 121 in a first operating mode according toFIG. 4 generates a first data state as bus state 402 with different buslevels for two bus wires 41, 42 of the bus line, and a second data stateas bus state 401 with the same bus level for the two bus wires 41, 42 ofthe bus line of bus 40.

In addition, transmitter 121 transmits the bits onto bus 40 at a higherbit rate for the temporal profiles of signals CAN FX_H, CAN FX_L in asecond operating mode, which includes data phase 452. CAN FX_H and CANFX_L signals may also be generated in data phase 452 with a differentphysical layer than with CAN FD. The bit rate in data phase 452 may thusbe increased even further than with CAN FD.

Check sum unit 15 from FIG. 3, in particular its header check sum block151, is used to compute and evaluate the check sum in the field forheader check sum H_CRC. In addition, check sum unit 15, in particularits frame check sum block 152, is used to compute and evaluate the checksum in the field for frame check sum F_CRC.

As mentioned above, a check sum for safeguarding the header of frame 450is formed, i.e., all bits from the start of frame 450 including the SOFbit to the start of header check sum H_CRC, including all dynamic, andoptionally, fixed, stuff bits up to the start of header check sum H_CRC.

In the present exemplary embodiment, communication control device 11, inparticular its check sum unit 15 or header check sum block 151, takesprecautions in computing header check sum H_CRC in order to eliminate anerror referred to as type B. Such an error may occur due to the dynamicstuff bits, which may occur up to the FXF bit of frame 450. The erroroccurs when stuff bits are erroneously inserted or removed due to errorsynchronizations caused by “glitches,” while the instantaneousintermediate result of check sum CRC has the value 0.

Communication control device 11, in particular its check sum unit 15 orheader check sum block 151, therefore selects the starting value forcomputing header check sum H_CRC in such a way that not all bits of theCRC generator register can be at “0” while a bit sequence withoutdetected stuff errors up to the FXF bit is being processed. Thus, thetemporary value of the computation of header check sum H_CRC up to theprocessing of the FXF bit cannot become 0 . . . 0. The starting value isthus to be set to a particular value, but not to 0 . . . 0, so that no 0. . . 0 value occurs in header check sum H_CRC up to the FDF bit.

In determining the starting value for computing header check sum H_CRC,communication control device 11, in particular its check sum unit 15 orheader check sum block 151, takes into account that a CAN FX userstation 10, 30 cannot transmit any arbitrary bit sequence up to the FXFbit. Communication control device 11, in particular its check sum unit15 or header check sum block 151, therefore determines the startingvalue under the following boundary conditions, namely,

-   -   that no more than five dominant bits or five recessive bits may        be transmitted in succession by the dynamic stuff bits, and    -   that certain bits of frame 450 have a fixed value, as described        above, and therefore are not variable.

The predetermined starting value may thus be dynamically configured bycommunication control device 11, in particular with the aid of softwarein check sum unit 15 or header check sum block 151.

Alternatively, the predetermined starting value may be permanentlystored in communication control device 11 once the starting value hasbeen determined, either by communication control device 11 or some otherdevice. Alternatively, the predetermined starting value may be selectedby an operator under the condition that the starting value is not equalto 0 . . . 0.

Thus, a type B error can no longer occur in user station 10.

The major advantage of the described procedure for computing thestarting value is that no additional bits are introduced into frame 450.The data overhead of frame 450 and the complexity of evaluating frame450 are thus reduced.

In addition, it might be necessary to increase the length of headercheck sum H_CRC and thus the order of the CRC polynomial to allow anappropriate H_CRC starting value to be found. Header check sum H_CRCwould thus be longer than would be necessary for detecting a certainnumber of normal bit flips, in which the bit state inadvertently changesdue to an error.

Furthermore, for frame 450, which uses an identifier ID including 11bits, communication control device 11, in particular its check sum unit15 or header check sum block 151, could use a different polynomial forheader check sum H_CRC than for frame 450, which uses an identifier IDincluding 29 bits. This has the advantage that the data overhead due toheader check sum H_CRC for frame 450, which uses an identifier IDincluding 11 bits, is smaller than for frame 450, which uses anidentifier ID including 29 bits.

Check sum unit 15, in particular its frame check sum block 152, alsoforms frame check sum F_CRC, as mentioned above. Check sum unit 15 mayapply one of the stated options. According to the following options 1and 2, frame check sum F_CRC in each case safeguards entire frame 450 upto frame check sum F_CRC.

Option 1: Frame check sum F_CRC is computed across entire frame 450.Thus, all bits beginning with and including the SOF bit up to the startof frame check sum F_CRC are included in the computation of frame checksum F_CRC. In addition, the dynamic stuff bits and optionally also thefixed stuff bits are included in the computation. Since header check sumH_CRC already safeguards the header of frame 450 against the type Berrors, frame check sum F_CRC does not have to do this again.

Option 2: Frame check sum F_CRC is computed across header check sumH_CRC and data field 455. Thus, all bits beginning with and includingthe first bit of header check sum H_CRC are included in the computationof frame check sum F_CRC. The fixed stuff bits are also optionallyincluded in the computation. Since header check sum H_CRC alreadysafeguards the header of frame 450, it is sufficient to include headercheck sum H_CRC in the F_CRC computation in order to safeguard entireframe 450.

Option 3: Frame check sum F_CRC safeguards only data field 455. Thus,all bits beginning with the first bit after header check sum H_CRC up tothe start of frame check sum F_CRC are included in the computation offrame check sum F_CRC. The fixed stuff bits are also optionally includedin the computation. Thus, frame check sum F_CRC safeguards only datafield 455. This is sufficient due to the fact that header check sumH_CRC already safeguards the header of frame 450. Frame check sum F_CRCand header check sum H_CRC together safeguard complete frame 450.

FIG. 6 shows a frame 450_1 according to a second exemplary embodiment inwhich CAN FX and CAN FD are compatible. In this exemplary embodiment,frame 450_1 and thus the CAN FX frame format are different from frame450 from FIG. 2, as described below. Only the differences from frame 450from FIG. 6 are described. In other respects, frames 450, 450_1 of thetwo exemplary embodiments are the same.

An S_C field is inserted into frame 450_1 prior to header check sumH_CRC. The number of transmitted dynamic stuff bits (stuff count) istransmitted in the S_C field. The S_C field may include 1 to n bits. Inthis case, i.e., for frame 450_1, a maximum of 3 dynamic stuff bitsoccur: i.e., n may be selected as 2. Alternatively, the transmission of“number of dynamic stuff bits modulo X” is possible in order to reducethe number of bits to be transmitted. X may be 2, for example.

However, due to this variant the data overhead of frame 450_1 is greaterin comparison to frame 450 from FIG. 2.

In one modification of frame 450_1, instead of the number of transmitteddynamic stuff bits (stuff count) a stuff compensator is inserted intothe S_C field. The stuff compensator includes 0 to m bits, where mcorresponds to the maximum number of dynamic stuff bits that may occurup to the FDF bit. The sum of dynamic stuff bits and stuff compensatorbits is always equal to m.

The stuff compensator ensures that the length of the frame header offrame 450_1 is constant. For example, in the case of 11 bits foridentifier ID, a maximum of three dynamic stuff bits may occur. Thus,m=3 would result for an identifier ID including 11 bits. In a frame450_1 including one dynamic stuff bit, the stuff compensator is 2 bitslong, since 3−1=2 bits applies. Data field 455 thus always begins aftera fixed number of bits after the start of the frame.

FIG. 7 shows a frame 4500 according to a third exemplary embodiment inwhich CAN FX and CAN FD are not compatible. In this exemplaryembodiment, frame 4500 and thus the CAN FX frame format are differentfrom frame 450 from FIG. 2, as described below. Only the differencesfrom frame 450 from FIG. 2 are described. In other respects, frames 450,4500 of the two exemplary embodiments are the same.

In general, when creating frame 4500 according to the present exemplaryembodiment only the fixed stuffing rule is used, so that a fixed stuffbit is to be inserted after a fixed number of bits. Alternatively,instead of only one stuff bit, 2 or more bits may also be inserted asfixed stuff bits. For a known value of data length code DLC, thisresults in a constant frame length or a constant length of frame 4500.This prevents various problems that are caused by dynamic stuff bits.

In frame 4500 according to the present exemplary embodiment, identifierID is no longer limited to 11 bits or 29 bits as with CAN FD. Number kof the bits of identifier ID may be freely selected. However, number kis alternatively settable to a fixed value. For a high net data rate, anID including k=8 bits is meaningful. This is sufficient to give eachuser station 10, 20, 30 of bus system 1 an adequate number of bus accesspriorities. Of course, some other value of k is selectable, depending onthe need and the number of various priorities in bus system 1.

Bits RRS, IDE, FDF, FXF of frame 450 from FIG. 2 are no longer necessaryin frame 4500 and are omitted. This saves 4 bits, so that the frameoverhead is reduced. The net data rate in bus system 1 is thusincreased.

End field EOF includes only 5 bits in frame 4500 when the NACK bit isdominant. In contrast, if the NACK bit is recessive, end field EOFincludes 3 bits. This ensures that 6 recessive bits are transmitted atthe end of frame 4500. This number of recessive bits cannot occur at anyother location in a valid frame 4500 when a fixed stuff bit is insertedafter 5 identical bits in arbitration phase 451. Alternatively, therecould be more than 6 bits. In particular, the number of EOF bits must beadapted to the number of bits after which a fixed stuff bit is inserted.

Interframe space IFS does not require a minimum length in frame 4500. Inparticular, interframe space IFS may have the length 0. In such a case,two frames 4500 are seamlessly transmitted in succession. However, aninterframe space IFS that includes 1 bit, for example, is alsomeaningful in order to increase the robustness of bus system 1 incomparison to the previously stated case. Due to the now 7 recessivebits between two frames 4500, a new user station at bus 40 maysynchronize more reliably.

Thus, no dynamic stuff bits occur for frame 4500. As a result, it is notnecessary to provide protection from the error type B described above.Therefore, field S_C from FIG. 6, used to detect error type B, is notrequired, so that the frame overhead is even further reduced. Headercheck sum H_CRC may optionally also be dispensed with, so that the frameoverhead is even further reduced. This increases the net data rate inbus system 1 even more.

For frame 4500, frame check sum F_CRC may thus be computed according toone of options 1 through 3, as described with regard to the firstexemplary embodiment, in which CAN FD compatibility is present.

All of the above-described embodiments of user stations 10, 20, 30, ofbus system 1, and of the method carried out therein may be used alone orin any possible combination. In particular, all features of theabove-described exemplary embodiments and/or modifications thereof maybe arbitrarily combined. Additionally or alternatively, in particularthe following modifications are possible.

Although the present invention is described above with the example ofthe CAN bus system, the present invention may be employed for anycommunications network and/or communication method in which twodifferent communication phases are used in which the bus states, whichare generated for the different communication phases, differ. Inparticular, the present invention is usable for developments of otherserial communications networks, such as Ethernet and/or 100Base-T1Ethernet, field bus systems, etc.

In particular, bus system 1 according to the exemplary embodiments mayalso be a communications network in which data are seriallytransmittable at two different bit rates. It is advantageous, but not amandatory requirement, that in bus system 1, exclusive, collision-freeaccess of a user station 10, 20, 30 to a shared channel is ensured, atleast for certain time periods.

The number and arrangement of user stations 10, 20, 30 in bus system 1of the exemplary embodiments is arbitrary. In particular, user station20 in bus system 1 may be dispensed with. It is possible for one or moreof user stations 10 or 30 to be present in bus system 1. It is possiblefor all user stations in bus system 1 to have the same design, i.e., foronly user station 10 or only user station 30 to be present.

The present invention described above may be further refined with regardto the introduction of different identifiers, as explained below andillustrated in FIG. 8.

The terms “message” and “frame” are used synonymously in thedescription.

FIG. 8 illustrates the refinement using different identifiers, startingfrom the frame format from FIG. 2. The refinement using differentidentifiers may be correspondingly applied in a manner completelyanalogous to the frame formats illustrated in FIG. 6 or FIG. 7.

Multiple identifiers are introduced into the CAN FX frame:

Priority ID:

The priority ID replaces or corresponds to identifier ID, alreadydescribed, in arbitration field 453 of the messages or frames 450,450_1, or 4500. The priority ID is preferentially used for the priorityof the bus access in the course of the arbitration.

MSG ID:

Message identification MSG ID, which may be transmitted in data field455, identifies the content of the message or the frame. Messageidentification MSG ID is optional.

TX ID:

Sender identification TX ID, which may be transmitted in data field 455,identifies the sender of the message or the frame. Sender identificationTX ID is optional.

VLAN ID:

Virtual network identification VLAN ID, which may be transmitted in datafield 455, contains forwarding information for the message or the frame.Virtual network identification VLAN ID is optional.

Advantages:

The stated introduction of multiple identifications has the followingadvantages over the conventional identifier with CAN FD:

Each of the listed identifications has the optimal length in order tooptimally fulfill the required identification or function. At the sametime, a high net data rate is achieved, on the one hand because onlythose bits that are absolutely necessary for the arbitration aretransmitted in the slow arbitration phase, and on the other hand,because only those optional identification types (MSG ID, TX ID, VLANID) that are required for the particular application may be used.

The order of optional identifications MSG ID, TX ID, and VLAN ID withinthe data field may also be selected differently from the order indicatedabove and illustrated in FIG. 8.

Description of the portions of the frame in FIG. 8 that are relevant forthis aspect of the present invention:

-   -   Priority ID        -   This ID corresponds to the frame ID for CAN FD.        -   For CAN FX it is referred to as “priority ID” due to the            fact that it primarily indicates the bus access priority.            The higher the priority, the earlier a frame wins the            arbitration at the bus.        -   In the example illustrated in FIG. 8, the CAN FX frame is            compatible with the CAN FD frame. This limits the length of            the priority ID to 11 or 29 bits. For a CAN FX frame that is            not compatible with CAN FD, the priority ID could have an            arbitrary length, for example 5 bits, in order to generate a            particularly low overhead. This has already been explained            in conjunction with the exemplary embodiments from FIGS. 2            and 7.    -   DLC: data length code        -   Data length code DLC indicates the number of bytes in the            data field (corresponding to data field 455 of the            illustrations in FIGS. 2, 6, and 7).        -   There are now two alternatives for use of the DLC:            -   A) Optional identifications MSG ID, TX ID, and VLAN ID                in the data field may be part of the data field; i.e.,                the DLC indicates the length of the data field including                optional identifications MSG ID, TX ID, and VLAN ID in                the data field. In other words, the first bytes of the                data field contain the IDs. This case is illustrated in                FIG. 8. However, this does not necessarily have to be                the first bytes. In this case, the application must have                knowledge of which identifications IDs are present in                the data field and what length they have.            -   B) Optional identifications MSG ID, TX ID, and VLAN ID                are not considered as part of the data field, and the                DLC indicates the length of the user data without                optional identifications MSG ID, TX ID, and VLAN ID.

Which of the optional identifications MSG ID, TX ID, and VLAN ID arepresent in a frame and what length they have may then be indicated byconfiguring the communication control device.

-   -   Additional identifiers (as part of the data field or separate)        -   MSG ID            -   The message ID identifies the content of the message or                the frame. With the aid of this ID, a reception node may                detect what information is in this frame. For example,                MSG ID=0×10 stands for the vehicle speed.            -   This ID is optional; i.e., it may also have the length                0.            -   The length of the ID is ideally settable in a bitwise                manner in the communication control device. For example,                16 bits would be a possible value for the length.        -   TX ID            -   The TX ID identifies the sender of the message or the                frame. This means that each transmission node uses one                (or multiple) exclusively assigned ID(s), and inserts                it/them into the frame during the transmission.            -   This ID is optional; i.e., it may also have the length                0.            -   The length of the ID is ideally settable in a bitwise                manner in the communication control device. For example,                8 bits would be a possible value for the length.        -   VLAN ID            -   The VLAN ID identifies the subnetwork in which this                message or this frame is to be visible, or in which this                message or this frame is to be relayed. For example, a                gateway may evaluate this VLAN ID and derive therefrom                in which other networks this message or this frame is to                be relayed.            -   This ID is optional; i.e., it may also have the length                0.            -   The length of the ID is ideally settable in a bitwise                manner in the communication control device. For example,                4 bits would be a possible value for the length.

Application of the various identifiers:

-   -   Priority ID        -   Each bus user (hereinafter also “node”) is exclusively            assigned at least one dedicated priority ID.        -   Each node ideally is exclusively assigned up to K priority            IDs. The up to K priority IDs allow up to K different            priorities (priority classes) to be defined. Each            message/each frame that transmits a node obtains a priority            ID that corresponds to the priority of the message/the            frame.        -   An example of a bus system that includes 4 nodes and a            maximum of K=3 priority IDs per node:

Priority IDs High Medium Low priority priority priority Comment Node 110 20 60 Node 2 11 21 61 Node 3 12 22 62 Node 4 Not 23 63 This nodetransmits assigned no high-priority messages, and therefore has nopriority ID of the class “high priority”

-   -   -   Each node optionally obtains multiple priority IDs in a            priority class. This means, for example, that node 1 for the            “medium priority” obtains priority IDs 20, 24, 28, and node            2 obtains priority IDs 21, 25, 29. If each node in a            priority class now selects the IDs according to a certain            rule or randomly, for example according to a “round robin”            process, for example, node 1 then is not continuously            superior to node 2 in the middle priority class; i.e., node            1 does not always have a higher priority. Fairness is thus            achieved within a priority class.        -   Optionally, if a message or a frame has already lost the            arbitration multiple times, according to a certain rule the            priority ID for this message or this frame is also exchanged            for a priority ID with higher priority, so that the message            has a better chance of winning the arbitration. In other            words, this means that the association of a priority ID with            messages may take place dynamically.

    -   MSG ID        -   Each piece of information to be transmitted via the bus            system is assigned one or multiple MSG IDs.        -   The MSG ID does not have to be exclusive for each node.            However, a certain MSG ID cannot be used for different            pieces of information.        -   If the MSG ID is exclusively assigned for a node, in            principle an application for the transmission of the TX ID            may then be dispensed with, since the MSG ID also implicitly            identifies the sender.

    -   TX ID        -   Each node is assigned at least one TX ID that is unambiguous            for the node. Two different nodes cannot receive the same TX            ID.        -   The or a TX ID assigned to the node is inserted into the            message.

    -   VLAN ID        -   With the VLAN ID, the transmission node determines in which            further connected networks the particular message is to be            relayed. Also, for example, a certain VLAN ID, such as the            VLAN ID of the value 0, could also mean a broadcast, i.e., a            relay into all connected networks.

1-12. (canceled)
 13. A user station for a serial bus system, comprising:a communication control device configured to control a communication ofthe user station with at least one other user station of the bus system;and a transceiver device configured to transmit a transmission signal,generated by the communication control device, onto a bus of the bussystem, so that for a message that is exchanged between user stations ofthe bus system, a bit time of a signal transmitted onto the bus in afirst communication phase is different from a bit time of a signaltransmitted in a second communication phase; wherein the communicationcontrol device is configured to generate the transmission signalaccording to a frame in which a field for a header check sum and a fieldfor a frame check sum are provided, the communication control devicebeing configured to provide an identifier in the frame which indicates apriority for transmitting the exchanged message onto the bus, and thecommunication control device being configured to provide at least onefurther identifier in the frame, the at least one further identifier, asa message identification, indicating content of data in a data field ofthe exchanged message, or as a sender identification, indicating atransmitting user station for the exchanged message, or as a virtualnetwork identification, indicating a piece of forwarding information forthe exchanged message.
 14. The user station as recited in claim 13,wherein the at least one further identifier is part of the data field,and a data length code indicates a length of the data field, taking intoaccount a length of the at least one further identifier.
 15. The userstation as recited in claim 13, wherein the at least one furtheridentifier is not part of the data field, and a data length codeindicates a length of the data field without taking into account alength of the at least one further identifier.
 16. The user station asrecited in claim 13, wherein a length of the message identification or alength of the sender identification or a length of the virtual networkidentification is settable in a bitwise manner in the communicationcontrol device.
 17. The user station as recited in claim 13, wherein theframe that is formed for the message is compatible with CAN FD.
 18. Theuser station as recited in claim 13, wherein in the first communicationphase, it is negotiated which of the user stations of the bus system ina subsequent second communication phase obtains, at least temporarily,exclusive, collision-free access to the bus.
 19. A method forcommunicating in a serial bus system, the method being carried out usinga user station of the bus system that includes a communication controldevice and a transceiver device, the method comprising the followingsteps: controlling, via the communication control device, acommunication of the user station with at least one other user stationof the bus system; and transmitting, via the transceiver device, atransmission signal, generated by the communication control device, ontoa bus of the bus system, so that for a message that is exchanged betweenuser stations of the bus system, a bit time of a signal that istransmitted onto the bus in a first communication phase is differentfrom a bit time of a signal that is transmitted in a secondcommunication phase, the communication control device generating thetransmission signal according to a frame in which a field for a headercheck sum and a field for a frame check sum are provided, thecommunication control device providing an identifier in the frame whichindicates a priority for transmitting the exchanged message onto thebus, and the communication control device providing at least one furtheridentifier in the frame, the at least one further identifier, as amessage identification, indicating a content of data in a data field ofthe exchanged message, or as a sender identification, indicating thetransmitting user station for the exchanged message, or as a virtualnetwork identification, indicating a piece of forwarding information forthe exchanged message.
 20. The method as recited in claim 19, whereinthe at least one further identifier is part of the data field, and adata length code indicates a length of the data field, taking intoaccount a length of the at least one further identifier.
 21. The methodas recited in claim 19, wherein the at least one further identifier isnot part of the data field, and a data length code indicates a length ofthe data field without taking into account a length of the at least onefurther identifier.
 22. The method as recited in claim 19, wherein alength of the message identification or a length of the senderidentification or a length of the virtual network identification issettable in a bitwise manner in the communication control device. 23.The method as recited in claim 19, wherein the frame that is formed forthe message is compatible with CAN FD.
 24. The method as recited inclaim 19, wherein in the first communication phase, it is negotiatedwhich of the user stations of the bus system in a subsequent secondcommunication phase obtains, at least temporarily, exclusive,collision-free access to the bus.